Many different modulation techniques are available for the transmission of digital data. Among these are differential phase shifted keyed modulation techniques. This invention relates to an improvement in differential phase shift keyed transmission of digital data signals by utilizing three different phases of a carrier frequency signal.
It is an object of this invention to show how both data and data synchronization information may be carried simultaneously in a single signal transmission.
It is also an object of this invention to permit the carrying of uniquely identifiable character or frame synchronization information within the transmitted data stream.
Other objects and advantages of the invention will become apparent from the following description.
It is noted that the invention may be utilized in a digital data modem which provides the interface to a coaxial transmission media of a time division multiple access bus communication system. The modem serves to transmit and receive information by modulating and demodulating the digital data. The tri-phase shift keyed modulation technique incorporated in the modem permits both data and data synchronization signals to be transmitted at a single frequency which are then differentiated by phase as opposed to encryption of the synchronization word.